Edson Porto da Silva

Constellation Shaping for WDM Systems Using 256QAM/1024QAM With Probabilistic Optimization

In this paper, probabilistic shaping is numerically and experimentally investigated for increasing the transmission reach of wavelength division multiplexed (WDM) optical communication systems employing quadrature amplitude modulation (QAM). An optimized probability mass function (PMF) of the QAM symbols is first found from a modified Blahut-Arimoto algorithm for the optical channel. A turbo coded bit interleaved coded modulation system is then applied, which relies on many-to-one labeling to achieve the desired PMF, thereby achieving shaping gains. Pilot symbols at rate at most 2% are used for synchronization and equalization, making it possible to receive input constellations as large as 1024QAM. The system is evaluated experimentally on a 10 GBd, 5 channels WDM setup. The maximum system reach is increased w.r.t. standard 1024QAM by 20% at input data rate of 4.65 bits/symbol and up to 75% at 5.46 bits/symbol. It is shown that rate adaptation does not require changing of the modulation format. The performance of the proposed 1024QAM shaped system is validated on all 5 channels of the WDM signal for selected distances and rates. Finally, it is shown via EXIT charts and BER analysis that iterative demapping, while generally beneficial to the system, is not a requirement for achieving the shaping gain.

Quaternary Polarization-Multiplexed Subsystem for High-Capacity IM/DD Optical Data Links

We demonstrate for the first time an intensity-modulated direct-detection link using four states of polarization. The four data-independent tributaries are each assigned distinct states of polarization to enable the receiver to separate the signals. Polarization rotation due to propagation over optical fiber is tracked and compensated with simple digital signal processing in Stokes space. Transmission below the forward error correction limit is shown for maximum net bitrates of 100 Gb/s (4 × 27 GBd) and 120 Gb/s (4 × 32 GBd) over 2-km standard single-mode fiber at a center wavelength of 1550 nm.

High speed PAM-8 optical interconnects with digital equalization based on neural network

We experimentally evaluate a high-speed optical interconnection link with neural network equalization. Enhanced equalization performances are shown comparing to standard linear FFE for an EML-based 32 GBd PAM-8 signal after 4-km SMF transmission.

WDM transmission of 3×1.12-Tb/s PDM-16QAM superchannels with 6.5-b/s/Hz in a 162.5-GHz flexible-grid using only optical spectral shaping

We demonstrated the transmission of 3×1.12-Tb/s superchannels (5×224-Gb/s PDM-16QAM) in 162.5-GHz flexible-grid, 6.5-b/s/Hz SE, using only optical spectral shaping, over SSMF-EDFA link. A maximum reach of 600-km with 3-ROADM passes was obtained employing nonlinear compensation.

Enhanced digital polarization demultiplexation via CMA step size adaptation for PM-QPSK coherent receivers

Fixed step size CMA can exhibit serious penalties due to rapid channel variations during coherent receiver polarization demultiplexing. We propose and experimentally demonstrate two CMA gain adaptation methods that improve dynamic equalizer tracking and convergence.

Wavelength conversion of QAM signals in a low loss CMOS compatible spiral waveguide

We demonstrate wavelength conversion of quadrature amplitude modulation (QAM) signals, including 32-GBd quadrature phase-shift keying and 10-GBd 16-QAM, in a 50-cm long high index doped glass spiral waveguide. The quality of the generated idlers for up to 20 nm of wavelength shift is sufficient to achieve a BER performance below the hard decision forward error correction threshold BER performance (<3.8 × 103), with an optical signal-to-noise ratio penalty of less than 0.3 dB compared to the original signal. Our results confirm that this is a promising platform for nonlinear optical signal processing, as a result of both very low linear propagation loss (<0.07 dB/cm) and a large material bandgap, which in turn ensures negligible nonlinear loss at telecom wavelengths.Optical wavelength conversion of high bandwidth phase-encoded signals in a high FOM 50cm CMOS compatible waveguide Francesco Da Ros, a) Edson Porto da Silva, Darko Zibar, Sai T. Chu, Brent E. Little, Roberto Morandotti, 5, 6 Michael Galili, David J. Moss, and Leif K. Oxenløwe 1) DTU Fotonik, Technical University of Denmark, DTU, Kongens Lyngby, 2800, Denmark, DK 2) Department of Physics and Materials Science, City University of Hong Kong 3) Xi’an Institute of Optics and Precision Mechanics, CAS, Xi’an, China PRC 4) INSR Énergie,Matériaux et Télécommunications, 1650 Blvd Lionel Boulet, Varennes (Québec), J3X1S2, Canada 5) Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054, China 6) National Research University of Information Technologies, Mechanics and Optics, St. Petersburg, Russia. 7) Centre for Microphotonics, Swinburne University of Technology, Hawthorn, VIC 3122, Australia

Widely Linear Equalization for IQ Imbalance and Skew Compensation in Optical Coherent Receivers

In this paper, an alternative approach to design linear equalization algorithms for optical coherent receivers is introduced. Using widely linear (WL) complex analysis, a general analytical model it is shown, where In-phase/quadrature (IQ) imbalances and IQ skew at the coherent receiver front-end are naturally included in channel equalization problem. Next, the problem of chromatic dispersion (CD) compensation after imbalanced and skewed coherent detection is analyzed. Based on the analytical models obtained it is demonstrated that, under the presence of such receiver front-end imperfections, the complexity of the channel equalization filter which is able to provide optimal performance, on the minimum mean square error sense, will scale proportionally to twice the complexity of CD compensation, if standard zero-forcing equalization of CD is applied as first equalization procedure. For the last, it is shown that, by applying the WL complex analysis, one can derive a complex-valued adaptive equalizer structure which is able to compensate for linear IQ-mixing effects at the receiver front-end. By extensive numerical simulations, the performance versus complexity of the proposed equalizer is shown to match the predictions of the analytical models derived.

Nonlinear compensation with modified adaptive digital backpropagation in flexigrid networks

We present a modified version of adaptive digital backpropagation based on EVM metric, and numerically access its performance in a flexigrid WDM scenario.

Focusing Over Optical Fiber Using Time Reversal

A time-reversal array in multimode fiber is proposed for lossless remotely controlled switching using passive optical splitters. The signal to be transmitted is digitally predistorted so that it is routed through the physical layer in order to arrive at only one receiver in an array. The system performance in the presence of an additive white Gaussian noise, modal group delay, and timing error is investigated numerically for single-mode fiber and 10-mode fiber. Focusing using a two-transmitter array and 44 km of single-mode fiber is demonstrated experimentally for 3-GBd QPSK signals with a bit error rate below the forward error correction limit.

Experimental analysis of pilot-based equalization for probabilistically shaped WDM systems with 256QAM/1024QAM

Pilot based equalization is studied in a 5×10 GBaud WDM transmission experiment. The equalization is independent of the modulation format and is demonstrated for 256/1024QAM with uniform and probabilistically optimized distribution using an optimized pilot insertion rate of 2–5%.